Self-propelled riding mowers are well-known. They typically comprise a cutting unit secured to the front of a traction unit. The operator sits on and is carried by the traction unit. The cutting unit usually includes one or more rigid steel blades rotated in horizontal cutting planes to sever grass or other vegetation at a pre-determined height above the ground. Such riding mowers are often known as rotary mowers since the blades revolve in a rotary fashion in the cutting unit. The assignee for the present application manufactures two such products which are typical of this class of riding mowers. These products are the Groundsmaster 52.RTM. and Groundsmaster 72.RTM. riding mowers.
The Groundsmaster 52.RTM. riding mower includes a frame that extends forwardly from the traction unit. This frame includes two lift arms. The lift arms can be used to raise or lower the frame between an upper transport position and a lower cutting position. The cutting unit is rigidly secured to the frame. The frame includes two caster wheels located in front of the cutting unit. The caster wheels roll over the ground surface to sense the ground contour. The height of cut is changed by changing the height of the caster wheels relative to the frame.
One disadvantage with the conventional Groundsmaster 52.RTM. riding mower has been the rigid attachment of the cutting unit to the frame. This does not allow a side-to-side floating action of the cutting unit relative to the frame. Thus, a bump in the ground surface which occurs between the caster wheels, and which does not therefore cause the caster wheels to change their elevation, will usually be scalped by the cutting unit. By scalped it is meant that the rotary blades of the cutting unit either cut the vegetation too closely to the ground or in some cases come in contact with the ground itself. This inability of the cutting unit to float freely from side-to-side is disadvantageous.
Various techniques have been used for allowing a cutting unit to float from side-to-side. One of these techniques is used on the Groundsmaster 72.RTM. Toro riding mower. In this product, the two lift arms are attached directly to the cutting unit using universal joint connections. Each lift arm is also independently movable at its point of attachment to the traction unit. The cutting unit is provided with four caster wheels which roll on the ground surface. The use of universal joints at the connection between the lift arms and the cutting unit allows the cutting unit to tilt side-to-side relative to the traction unit and the lift arms. Such a cutting unit has superior anti-scalping properties.
The universal joint solution to the problem of giving a cutting unit a side-to-side tilt is somewhat expensive. Thus, it may be somewhat uneconomic for a product of smaller size, such as the Groundsmaster 52.RTM.. It would be advantageous to have a simpler solution for this problem, which would be less expensive, but which would give equally good results.